The disclosures herein relate generally to computer systems and more particularly to a ground clip for connecting a ground plane of a printed wiring board to a computer chassis.
There have been many conventional mechanisms used to electrically connect a chassis to a ground conductor. One popular mechanism involves placing a screw through a printed wiring board (PWB) and into the chassis. At the upper surface of the board is a conductive solder pad, onto which the lower surface of the screw head is designed to abut. The solder pad is coupled to the ground conductor through a via. The via is configured on the exposed planar surface of the board and/or is buried within the board itself. By tightening the screw into the chassis, the backside surface of the screw head contacts the solder pad resulting in an electrical path from the chassis to the ground conductor by way of the screw, solder pad and via.
It is necessary that not only the hole through the board into which the screw is placed be aligned with the hole in the chassis, but it is also necessary that a via be reliably formed between the solder pad arranged on the upper surface of the board and all ground conductors formed upon and/or within the board. Placement of the screw is not only tedious and time consuming, but also must be performed with extreme care. Any slip of the tightening tool from the screw head to the board upper surface could not only damage the printed conductors or vias arranged thereon, but could also, in extreme cases, pierce or crack the insulative glass fiber laminate of the board.
Still further, tightening of the screw head backside surface upon the solder pad can dislodge solder particles from the solder pad which can migrate from the solder pad and possibly lodge between printed conductors, edge-board contacts and/or receptor contacts. Vibration or any type of relative motion between the screw head and underlying board caused, for example, by an operable electronic device or periodic movement of that device can, over time, result in reliability problems. Movement of the electronic device may cause the screw to loosen in a counter fashion or, more likely, movement of the device may dislodge solder underneath the head as the head moves relative to the solder pad. Movement of the head causes the head to sweep the relatively soft solder from the pad, resulting in eventual separation between the head and the solder pad.
Any separation between the grounded screw and the solder pad will force an open circuit therebetween. An improperly grounded ground conductor can affect the operability of each and every component coupled to the ground conductor. It is therefore important that an alternative chassis-to-ground conductor connection be made which is less labor intensive, is less prone to user error, is less susceptible to solder being dislodged during assembly and operation, and is generally more reliable.
Failure to provide a good ground path between a printed wiring board and the computer chassis results in poor electromagnetic interference (EMI) performance. In the past, a combination of screws and solder pads on the PWB have been used to provide a ground path from the PWB to the computer chassis. These methods, although cost effective, are neither repeatable nor reliable. Furthermore, their effectiveness is dramatically reduced each time the PWB is installed and removed.
One attempt at providing an improvement is disclosed in U.S. Pat. No. 5,647,748. This approach provides a printed circuit board grounding clip having upwardly extending retainers and downwardly extending legs. The legs are designed to insert within plated through-holes of a variable thickness printed circuit board. The upwardly extending retainers terminate as a spaced pair of flanges which frictionally receive and electrically couple with a hook. The hook extends from the chassis of an electronic device, through a slot within the PWB and between the spaced flanges. Accordingly, the hook and ground clip form an electrical conduit between a ground supply connected to the electronic device chassis and a ground conductor formed within the PWB. Chassis-to-ground conductor attachment is performed during assembly of the board to the chassis backplane. Attachment can be quickly and easily reversed to allow board re-work, without requiring placement of heat upon the board. The present attachment mechanism further avoids user-inserted fasteners and the reliability problems they present.
Although the above-described grounding clip represents a substantial improvement, there are limitations. First, the installed cost is high when compared to previous methods and devices. Also, the clips are installed into the PWB by hand which increases labor cost. In addition, the clips are prone to being deformed during installation which affects their performance. Further, due to their complex configuration, a plurality of these clips stored together, tend to become entangled and are difficult to separate. If care is not taken during separation, damage to the clips may easily occur.
Therefore, what is needed is a surface mount grounding clip which is relatively non-complex, physically robust, and can be used in pick-and-place assembly used for other components being installed in the manufacturing process.